Familial occurrence of Behçet's disease was studied in the Uveitis Survey Clinic of Hokkaido University Hospital. Eighteen patients in the nine families had familial occurrence of this disease. Male to female ratio was 0.28 in the familial cases, which was significantly higher than in the sporadic cases. Familial occurrence was most frequently seen among siblings. Most patients, including all of the females, belonged to the complete type. They had typical ocular lesions and exhibited bilateral uveoretinitis with poor visual prognosis, particularly in the females. The frequency of HLA-B5 was 92% in the familial patients, which was significantly higher than in the normal controls and the sporadic cases. It is probable that patients with familial occurrence of this disease have poorer prognosis with stronger immunogenetic backgrounds.